Filter device

ABSTRACT

The invention relates to a filter device with a filter housing (10), in which at least two filter elements (12, 14), with differing filter grades of filter material (16), are arranged, which are each partially separated from each other by a separating device (18), with a through channel (24) of predetermined cross-section for a hydraulic connection between neighbouring filter chambers (20, 22), which are arranged prior to the filter materials (16) in the flow direction of the fluids for filtering. According to the invention, the filter device permits a combination of a so-called main- and a so-called side-stream filter in the smallest possible space, whereby very good purity levels for the filtered fluid are nevertheless achieved.

[0001] The invention relates to a filter device with a filter housing in which are mounted at least two filter elements with filter materials of different filtration grades, which are partly separated from each other by a separating device, which has a passage point of assignable cross-section for a fluid-conducting connection of adjacent filter spaces which are situated upstream from the filter materials in the direction of flow of the fluid to be cleaned.

[0002] The features referred to permit combination of a so-called primary flow filter with a secondary flow filter in one filter housing; in view of the different filtration grades of the filter materials employed, the filter with the coarser filtration grade serves as primary flow filter and thus receives the greater part of the flow volume to undergo particle removal, while the filter element with the finer filtration grade in contrast removes particles from a smaller flow volume. Such cleaning by means of primary and secondary flow filters results in very good cleaning quality even though the greater share of the volume of the fluid to be cleaned is subjected to coarse filtration; the filter device claimed is very compact in structure and in general requires a small number of structural components. This condition both increases reliability in operation and keeps manufacturing, installation, and maintenance costs low. High precision of current volume division can be achieved for primary and secondary flow filtration by the passage point claimed of assignable cross-section inside the separation device; this improves the quality of filtration of the fluid to be cleaned.

[0003] In a preferred embodiment of the filter device claimed for the invention the filter housing has an inlet point for the fluid to be cleaned and an outlet point for the cleaned fluid; the filter element with coarser filtration grade is mounted adjacent to the inlet point and the filter point with finer filtration grade opposite the former, adjacent to the outlet point. As a result, the flow of fluid through the filter from the inlet point to the outlet point is especially favorable.

[0004] In another preferred embodiment of the filter device claimed for the invention the separating device has a separating plate which is connected to the filter housing so as to effect sealing and the latter is divided into two adjacent housing subspaces, the ends of the adjacent filter elements being in contact with the separating plate, which is provided with an additional passage point for connection of the interiors of these filter elements. One housing subspace containing the filter element with coarser filtration grade has the filter space which is connected to the inlet point so as to conduct fluid, while the other housing subspace containing the filter element with finer filtration grade has the other filter space, which is connected by way of this filter element to the outlet point so as to conduct fluid. In addition, one filter space is connected by way of the passage point to the other filter space so as to conduct fluid. An especially compact structure of the filter device as a whole is obtained; such a structure does not require a complete filter housing of its own, but is also suitable for installation on the tank side with an integrated filtering jug.

[0005] In another especially preferred embodiment of the filter device claimed for the invention, the filter elements are mounted coaxially with each other inside the filter housing and are introduced into the element receptacles with their free ends facing away from each other. The filter materials of the filter elements preferably rest on support elements, which are modular in structure and can be adapted to various longitudinal dimensions of the filter elements. In this way a modular structure can be achieved on the whole for the filter device claimed for the invention; this structure can be adapted cost effectively to a wide variety of applications.

[0006] In another especially preferred embodiment of the filter device claimed for the invention, one passage point consists of a curved passage segment and the other passage segment has a throttle point such that the flow resistance is increased for the filter element with the coarser filtration grade. A corresponding throttle function is also assigned to the first passage point so as thereby to ensure the effectiveness of the secondary flow filter independently of the actual situation as regards fouling of the primary flow filter. In particular, the volume flows inside the filter device throttle points claimed may be coordinated so that reasonable division into primary flow and secondary flow filtration is achieved. As regards the throttle point, the additional passage point is preferably in the form of a fluid valve which applies an assignable closing spring pressure to the closing element in the direction of the additional passage point. As a result, a kind of preloading situation arises for the housing subspace with the filter element with coarser filtration grade and the fluid to be filtered is forced, as a function of the preloading selected, to pass appropriately through the first passage point acting as throttle point into the partition between the housing subspaces for secondary flow filtration.

[0007] In another preferred embodiment of the filter device claimed for the invention, at least the filter element with the coarser filtration grade is provided with a bypass valve. If in this instance complete clogging of the primary flow filter occurs, the bypass valve opens and supply of hydraulic fluid continues to be ensured; this is important if the device is appropriately inserted upstream from hydraulic machine tools or devices. However, the secondary flow filtration is optionally continued only to a limited extent regardless of the bypass situation. Preferably provision is also made such that at least one of the filter materials, preferably the filter material with the finer filtration grade, possesses moisture absorption properties. As a result, harmful moisture can be removed from fluid circulation by way of the filter device in primary and secondary flow filtration.

[0008] It has been found to be especially advantageous to design the passage points so that one part by volume which flows as secondary flow through the filter element with the finer filtration grade corresponds to eight to ten parts by volume in the primary flow which moves through the filter element with the coarser filtration grade.

[0009] The filter device claimed for the invention is described in detail in what follows with reference to the drawing, in which, in outline and not drawn to scale,

[0010]FIG. 1 shows a longitudinal section through the filter device as installed;

[0011]FIG. 2 a longitudinal section through the primary and secondary flow filter units as shown in FIG. 1;

[0012]FIG. 3 an enlarged top view of the separating device shown in FIGS. 1 and 2.

[0013] The filter device shown in FIG. 1 has a filter housing identified as a whole by 10. Two filter elements 12,14 are mounted one above the other in the filter housing. The filter elements in question 12,14 are characterized by filtration grades differing from each other. These filtration grades may be determined by use of different filter materials 16 or the same filter materials 16 are used but have different permeability values. The filter materials 16 may be in the form of hollow cylinders, but preferably in that of pleated filter matting, that is, matting folded like an accordion. In particular, filter materials 16 of a plastic substance may be employed in this application.

[0014] The two filter elements 12,14 are partly separated from each other spatially and with respect to external conduct of fluid by a separating device 18. An enlarged top view of the separating device 18 in question is presented in FIG. 3. For a fluid-conducting connection between the two adjacent filter spaces 20,22, however, the separating device in question has a passage point 24 upstream from the filter materials 16 in the direction of flow of fluid proper inside the filter device for the fluid to be cleaned. The filter housing 10 has an inlet point 26 for the fluid to be cleaned or filtered and an outlet point 28 for the fluid cleaned. Provision is also made such that the filter element 12 with the coarser filtration grade is mounted on the opposite side adjacent to the inlet point 26 in question, while the filter element 14 with the finer filtration grade is mounted on the opposite side adjacent to the outlet point 28. Both the inlet point 26 and the outlet point 28 are in the form of an inlet or outlet flange, the flanges in question being connected to the housing proper 10 by way of appropriate screw connections. The flange-like inlet point 26 may be connected to a fluid feed carrying fouled fluid inside a hydraulic circuit and tapers in extension so as to promote fluid inlet flow in the direction of the filter space 20.

[0015] In addition, the inlet point 26 is mounted more closely adjacent to the separating device 18 in the filter housing 10 than opposite the upper cover plate 32 of the filter housing 10 in question. The cover plate 32 is in turn connected by way of the screw connection not shown to the rest of the hollow cylindrical filter housing 10 and is sealed from this hollow cylinder wall by a conventional O-ring. The filter device may be ventilated by way of a sealing connection 34 on the upper end of the cover plate 32, or, for example, may be connected to a fluid fouling indicator not shown. In any event, after removal of the cover plate 32 it is possible to replace the filter unit itself containing filter elements 12 and 14 with a new unit when fouling reaches a particular level. In addition, the cover plate 32 has on its inner side mounting connectors 36 pointing inward which may be joined together in one piece in the form of a connector ring.

[0016] The separating device 18 consists essentially of a separating plate 38 which is connected to the interior of the filter housing 10 to effect sealing. For this purpose the separating plate 38 has a grooved annular channel 40 extending over its outer circumference, into which channel a conventional O-ring 42 is introduced to effect sealing. The separating plate 38 is preferably in the form of an injected plastic element and thus can be cost effectively manufactured. On the basis of the separating plate 38 in question the filter housing 10 is divided into two adjacent housing subspaces 44,46; the adjacent filter elements 14,16, with their ends facing each other as shown in FIG. 1, are frontally in contact with the separating plate 38 which is provided for connection of the interiors 48 of these filter elements 12, 14 to another passage point 50. One housing subspace 44 with the filter element 12 with the coarser filtering grade has the filter space 20, which is connected directly to the inlet point 26 so as to conduct fluid. The other housing subspace 46 with the filter element 14 with the finer filtering grade, on the other hand, has the other filter space 22, which in turn is connected by way of this filter element 14 to the outlet point 28 so as to conduct fluid. The filter elements 12,14 are mounted coaxially with each other inside the filter housing 10, that is, along the common longitudinal axis 52.

[0017] The longitudinal dimension selected for the upper filter element 12 as seen in the line of sight to FIGS. 1 and 2 is somewhat larger than that of the subjacent other filter element 14. In addition, the free ends of the filter elements 12,14 facing away from each other are introduced into element receptacles 54, which in turn are connected to support pipes 56 on the inside of the respective filter element 12,14. The support pipes in question 56, in order to form support elements, have individual support leaves 58, which in turn between themselves delimit free fluid passage points. The support pipes 56 may be built in modular form, that is, they may consist of individual segmental elements that may be joined to each other, elements which may be mounted in sequence as a function of the longitudinal dimension required. In addition, the support pipes 56 are in the form of plastic materials and internally have support studs 60 extending diametrically toward each other. The associated structure of support pipes 56 is known in the state of the art, so that no detailed discussion of the subject is needed at this point. The support studs 60 may in any event impart a specific direction to the flow of fluid inside the respective filter element 12,14; this favors energy conservation in filtration operation. The support studs 60 in any event do not hamper passage of fluid from the filter element 12 into the following passage point 50 or transition of the interior 48 of the filter element 14 in the direction of the curved flange-like outlet point 28. The filter elements 12,14 are cylindrical in form and have hollow cylindrical interiors for conduct of fluid.

[0018] On the ends adjacent to each other the filter elements 12,14 are received correspondingly into an annular recess 62 in the separating plate 38, which for this purpose has a corresponding receptacle extension on the side of the external circumference, that is, one which extends upward and downward. In the direction of the interior the filter elements 12,14 are supported again by way of the end areas of the support pipes 56, which in this area are in contact with the separating plate 38. The ring channel 40 is in turn fastened to the annular recess 62 and is reinforced by diametrically opposite studs 6 and 64. As is to be seen from FIG. 3 in particular, the passage point 24 is in the form of a curved passage segment which extends between two adjacent connection studs 64. The other passage point 50 in any event forms a throttle point such that the flow resistance is increased for the filter element 12 with the coarser filtration grade. This throttle point is in particular in the form of a fluid valve 66 which presses the closing element 68 in the direction of the additional passage point 50 with an assignable spring closing pressure. The closing element 68 has guide flanges 70 distributed on the circumference side which permit precise control of the closing element 68 inside the lower support 56. In addition, a support plate 72 of the fluid valve 66 is rigidly connected to the lower support pipe 56 and a closing spring 74 in the form of a pressure spring rests with its one of its free ends against this support plate 72 and with its other free end on a radial recess in the closing element 68 of the fluid valve 66.

[0019] The fluid valve 66 is shown in its closed position in FIGS. 1 and 2. The lower end positioned above it of the upper support pipe structure 56 is shown in outline; the support flanges 60 of the upper support pipe 56 do not in any event disrupt the operation of the fluid valve 66. The fluid valve 66 is provided with an assignable closing pressure which results in increase in the preloading pressure in the interior 48 of the upper filter element 12, with the result that the fouled fluid which passes through the corresponding filter material 16 is slowed by the increased preloading pressure and the tendency of the fouled fluid to flow through the first passage point 24 in the separating plate 38 to the additional filter element 14 with finer filtration grade becomes greater. This accordingly prevents occurrence of filtration in the primary flow only by way of the upper filter element 12, with hardly any filtration in the secondary flow by way of the lower filter element 14.

[0020] The filter element 12 with the coarser filtration grade is provided on its upper end with a bypass valve 76 in order to prevent operational failures as soon as the primary flow filter with the upper filter element 12 becomes completely clogged. In such a case the bypass valve 76 then opens and permits flow of the uncleaned fluid in the primary flow by way of the interiors 48 of the upper filter element 12 and lower element 14 to the outlet point 28. The bypass valve 76 is comparable to the fluid valve 66 in structure, so that what has been said applies to the bypass valve 76 as well. In order to be able also to eliminate moisture from the fluid, the filter material 16 of the lower filter element 14 has moisture-absorbent layers. The filter material 16 of the lower filter element 14 may also consists entirely of moisture-absorbent layers.

[0021] The filter elements 12 and 14 are geometrically more or less identical except for their length and filtration grades, that is, internal and external diameters correspond to each other. In addition, the filter elements 12, 14, together with the associated valves 66 and 76 and with their support pipes 56 and the support plate 38 form one structural unit, which as such may be replaced in its entirety by a new such unit; replacement is effected by way of the upper cover plate 32. The structural unit in question may be disposed of in environment-friendly fashion, incinerated, or recycled. So that the structural unit in question will also be retained securely in the housing 10, not only is support provided by way of the separating plate 38 on the housing side, but also there is provided in the area of the lower outlet point 28 a ring-shaped filter element receptacle 78 onto which the structural unit may be slipped by its lower filter element 14. The interior 48 of the lower filter element 14 is sealed fluid-tight from the lower filter space 22 by an O-ring seal. The filtration grade selected for the filter materials 16 is such that a coarse filtration grade value of 20 μm, for example, is selected for the upper filter element 12, while the lower filter element has a relatively fine filtration grade of, for example, 2 μm.

[0022] In any event, with the filter device claimed for the invention a primary flow filter 12 is accommodated with a secondary flow filter 14 in a filter housing 10 having only one inlet 26 and one outlet 28. The filter housing 10 may also consist exclusively of one compartment (this design is not shown), for example, if use in a tank with integrated filter cup is involved. The division into primary and secondary flow filters may be even further graduated, with more than two filter elements 12,14 (not shown) positioned in parallel being mounted in sequence. More finely graduated filtering capabilities may accordingly be provided for multiply separable volume flows. Again, the filter elements may in turn be designed to be in multiple parts, to the extent that this should be necessary out of considerations of practicability. In any event, the filter device illustrated makes it possible to cause a hydraulic flow of large volume of a relatively coarse filtration grade, for example, 20 μm absolute, and a hydraulic flow of low volume, for example 2 μm absolute, to flow through the device in parallel. The volume flows are coordinated by internal flow control by the orifices or throttles referred to in relation to the passage points 24 and 50. Introduction of additional throttles or orifices as a function of the flow control desired would also be possible.

[0023] In order to ensure efficiency for the secondary flow filter 14 independently of fouling of the primary flow filter 12, the throttle device in question is integrated into the outlet of the primary flow filter 12 and in the housing 10 between the upper and lower parts of the filter element. The filter device makes possible a compact operating, installation, and service unit to be provided for applications both in the high-pressure and the low-pressure area (in return-flow and in secondary-flow lines).

[0024] In the embodiment illustrated the passage points 24,50 are in any event designed so that for one part by volume flowing in the secondary flow through the filter element 14 with finer filtration grade there are to eight to ten parts by volume flowing in the primary flow through the filter element 12 with the coarser filtration grade. For the secondary flow operation in question, one fouled quantity of flow from the upper filter space 20 is diverted from the primary flow direction by way of the passage point 24 in the separating plate 38 and in this way transferred to the lower filter space 22 for finest filtering by the secondary flow filter 14. All fluid components filtered by the filter materials 16 in any event reach the outlet side 28 of the device by way of the interiors 48 of the filter elements 12,14. 

1. A filter device with a filter housing (10) in which are mounted at least two filter elements (12,14) with filter materials (16) of different filtration grades separated from each other by a separating device (18), which has a passage point (24) of assignable cross-section for a fluid-conducting connection between adjacent filter spaces (20,22) which are mounted in the direction of flow of the fluid to be cleaned upstream from the filter materials (16).
 2. The filter device as specified in claim 1, wherein the filter housing (10) has an inlet point (26) for fluid to be cleaned and an outlet point (28) for cleaned fluid and wherein the filter element (12) with the coarser filtration grade adjacent to the inlet point (26) and the filter element (14) with the finer filtration grade adjacent to the outlet point (28) are mounted opposite each other.
 3. The filter device as specified in claim 1 or 2, wherein the separating device (18) has a separating plate (38) which is connected to the filter housing (10) so as to effect sealing and the latter is divided into two adjacent housing subspaces (44,46) and wherein the ends facing each other of the adjacent filter elements (12,14) are in contact with the separating plate (38) which is provided for connection of the interiors (48) of these filter elements (12,14) to another passage point (50).
 4. The filter device as specified in claim 3, wherein the one housing subspace (44) with the filter element 12 of coarser filtration grade has a filter space (20) which is connected to the inlet point (26) so as to conduct fluid, and wherein the other housing subspace (46) with the filter element (14) with the finer filtration grade has the other filter space (22), which is connected by way of this filter element (14) to the outlet point (28) so as to conduct fluid.
 5. The filter device as specified in one of claims 1 to 4, wherein the filter elements (12, 14) are mounted coaxially with each other inside the filter housing (10) and are guided into element receptacles (54) by their free ends which face away from each other.
 6. The filter device as specified in claim 5, wherein the filter materials (16) of the filter elements (12,14) are supported by support elements (56, 58, 60) which are modular in structure and may be adapted to filter elements (12,14) of varying longitudinal dimensions.
 7. The filter device as specified in one of claims 3 to 6, wherein one outlet point (24) consists of a curved passage segment and wherein the other outlet point (50) has a throttle point such that the flow resistance for the filter element (12) with the coarser filtration grade is increased.
 8. The filter device as specified in claim 7, wherein the throttle point is in the form of a fluid valve (66) which presses against the closing element (68) in the direction of the other passage point (50) with an assignable spring closing pressure.
 9. The filter device as specified in one of claims 1 to 8, wherein at least the filter element (12) with the coarser filtration grade is provided with a bypass valve (76) and wherein at least one of the filter materials (16) possesses water-absorption properties.
 10. The filter device as specified in one of claims 3 to 9, wherein the passage points (24,50) are so designed that for one part by volume which flows in the secondary flow by way of the filter element (14) with the finer filtration grade eight to ten parts by volume reach the primary flow by way of the filter element (12) with the coarser filtration grade. 